gh-119132: Remove "experimental" tag from the CPython free-threading. (gh-135550)

* gh-119132: Remove "experimental" tag from the CPython free-threading build

* Address code review

Co-authored-by: Hugo van Kemenade <1324225+hugovk@users.noreply.github.com>

* Add NEWS.d

* Regen configure.ac

* Update doc

* Update

* Update

* Update

* Update Doc/howto/free-threading-python.rst

Co-authored-by: Peter Bierma <zintensitydev@gmail.com>

* Update ctypes.rst

* Update

* Update Doc/howto/free-threading-python.rst

Co-authored-by: T. Wouters <thomas@python.org>

* Apply suggestions from code review

Co-authored-by: T. Wouters <thomas@python.org>
Co-authored-by: Hugo van Kemenade <1324225+hugovk@users.noreply.github.com>

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Co-authored-by: Hugo van Kemenade <1324225+hugovk@users.noreply.github.com>
Co-authored-by: Peter Bierma <zintensitydev@gmail.com>
Co-authored-by: T. Wouters <thomas@python.org>